1. Field of the Invention
The present invention relates to a serial recording apparatus having recording means movable along the passage through which the recording sheet is moved. More particularly, the present invention relates to a recording apparatus capable of conveying the recording means and the recording sheet by one driving source.
2. Description of the Prior Art
Hitherto, in accordance with the wide use of word processors, a variety of printing devices have been developed. A daisy wheel type printing device has been available which is arranged in such a manner that a daisy wheel and a hammer are mounted on a carriage which is movable in the recording direction. When the daisy wheel is rotated, a desired type is selected, the type being then struck by the hammer. As a result, the ink on an ink ribbon is transferred to a recording sheet so that the data can be recorded.
In the above-described printing apparatus, a plurality of motors are employed to operate each of the components in such a manner that a wheel motor is used to rotate the daisy wheel, a ribbon motor is used to supply the ink ribbon, a carriage motor is used to move the carriage and a conveyance motor is used to convey the recording sheet.
However, the use of a plurality of motors to operate each of the components give rise to a problem in that the number of elements is unnecessarily increased. As a result, the manufacturing cost is excessive and the size of the apparatus cannot be reduced.
Furthermore, a major portion of the printing apparatus is arranged to move the carriage in a unit of one character (=10/120 inch) or a half character (=5/120 inch) to print each character. Therefore, information included in a work area which shows the present position of the carriage, that is, the carriage which has been moved in a unit of the half character, that is, 5/120 inch as an alternative to the unit of 1/120 inch which is the minimum resolution of the printing apparatus.
If the movement of the carriage and the conveyance of the sheet are performed by one driving source as described above, the amount of movement of the carriage at the time of conveying the sheet is determined by the gear ratio in the transmission from the driving source to the sheet conveyance device and the amount of the movement of the sheet. Therefore, the above-described value is not always a unit equal to a half character.
Therefore, the carriage position is displaced by a degree less than the half character with each conveyance action of the sheet. However, the above-described displacement cannot be corrected in an apparatus having no means for moving it by a degree smaller than the half character. If the minimum resolution of the carriage is changed into a unit of 1/120 inch in order to correct the displacement, the mechanism becomes too complicated. The reason for this lies in that one line of print is constituted by 120 characters in the case of a printing apparatus having one line of print equal to 10 inches in length. Therefore, the carriage can be positioned at 240 positions when movable in half character units. The numeral of 240 can be expressed by a variable of one byte. However, when the carriage is movable in 1/120 inch units, 1200 positions exist, the numeral 1200 being able to be expressed by a variable of 2 bytes. That is, the present position of the carriage, the destined position, and a variety of local operations variables must be converted from conventional 1-byte variables to 2-byte variables. Furthermore, that conversion must meet the following conditions:
(1) The RAM has an empty region in which the size of the variable can changed.
(2) The method of processing all of the portions using the above-described variable must be changed from the 1-byte operation to the 2-byte operation.
(3) The ROM has an empty region in which the above-described change (2) can be performed.
As a result, it is difficult to change the minimum resolution of a printing apparatus from 5/120 inch to 1/120 inch.